An artificial amino acid radiopharmaceutical for single photon emission computed tomographic study of pancreatic amino acid transports 123I-3-iodo-alpha-methyl-L-tyrosine.

123I-3-iodo-alpha-methyl-L-tyrosine (123I-L-AMT) was selected and its characteristics on pancreas accumulation, metabolic selectivity and metabolic stability of 125I-L-AMT were studied. The studies on rat tissue slice as well as mouse biodistribution proved very high accumulation of 125I-labeled L-AMT in the pancreas, which was remarkably inhibited by the active transport inhibitor, ouabain. 125I-L-AMT does not enter into protein synthesis and general amino acid catabolism. Moreover, 125I-L-AMT was very stable against enzymatic deiodination. Thus, the above studies indicated that the 123I-labeled L-AMT was an "artificial amino acid" radiopharmaceutical to be used for the selective measurement of the membrane amino acid transport rate in the pancreas.